1. Technical Field
The present invention pertains to the field of jet technology, primarily to liquid-gas ejectors for producing a vacuum during evacuation of various gaseous and gas-vapor mediums.
2. Background Art
An ejector is known, which comprises a steam nozzle, a mixing chamber, converging in the flow direction, with a throttle and a diffuser (see, Sokolov E. Y. and Zinger N. M., xe2x80x9cJet Apparatusesxe2x80x9d, Moscow, xe2x80x9cEnergoatomizdatxe2x80x9d Publishing house, 1989, pages 94-95).
Ejectors of this type are widely adopted for evacuation of gas-vapor mediums in the condenser units of steam turbines and in steam-ejector refrigeration units.
However efficiency of these ejectors is relatively low in cases when the evacuated gaseous mediums contain a lot of condensable components.
The closest analogue of the ejector introduced in the present invention is a liquid-gas ejector comprising a liquid nozzle and a mixing chamber (see, Sokolov E. Y. and Zinger N. M., xe2x80x9cJet Apparatusesxe2x80x9d, Moscow, xe2x80x9cEnergoatomizdatxe2x80x9d Publishing house, 1989, pages 213-214).
Such ejectors are used in power engineering as air-ejector devices of condenser units, in water deaeration vacuum systems, for vacuumization of various reservoirs. Character of the given ejectors is the fact that while evacuating a steam-air mixture the steam contained in the mixture is condensed and therefore a water-air mixture is compressed in the mixing chamber (if water is used as the liquid medium fed into the nozzle).
But the operational effectiveness of these ejectors is not high enough because performance of the ejector significantly depends on the distance between the outflow face of the nozzle and the inflow face of the mixing chamber.
The problem to be solved by the present invention is an increase in efficiency of a liquid-gas ejector comprising a nozzle and a mixing chamber by optimization of the distance between the outflow face of the nozzle and the inflow face of the mixing chamber.
The stated problem is settled as follows: in a liquid-gas ejector comprising a nozzle and a mixing chamber the distance between the outlet section of the nozzle and the inlet section of the mixing chamber is determined from the following formula:   L  =      k    ·                            G          ⁢                      xe2x80x83                    ⁢          α                μ            
where
Lxe2x80x94distance between the outlet section of the nozzle and the inlet section of the mixing chamber (mm);
kxe2x80x94design factor, ranging from 0.001 to 0.3;
xcex1xe2x80x94ratio of the surface area of the minimal cross-section of the active nozzle to the surface area of the minimal cross-section of the mixing chamber;
Gxe2x80x94liquid flow rate through the nozzle (g/sec);
xcexcxe2x80x94coefficient of resistance of the nozzle (g/sec*mm2), amounting from 0.5 to 1.1.
Experimental research has shown, that the distance from the outlet cross-section of a nozzle of a liquid-gas ejector to the inlet cross-section of a mixing chamber of the ejector exerts significant influence on the effectiveness of evacuation of a gaseous medium by the liquid-gas ejector. It was determined that optimal value of this distance depends mainly on the liquid flow rate and coefficient of resistance of the nozzle.
The coefficient of resistance of a liquid-gas ejector nozzle is calculated by the following mathematical expression:   μ  =      G                            2          ⁢                      F            c                    ⁢          gP                γ            
where
xcexcxe2x80x94coefficient of resistance of the nozzle (g/sec*mm2),
Gxe2x80x94liquid flow rate through the nozzle (g/sec);
Fcxe2x80x94surface area of the minimal cross-section of the nozzle;
gxe2x80x94acceleration of gravity;
Pxe2x80x94pressure of the liquid fed into the nozzle;
xcex3xe2x80x94density of the liquid fed into the nozzle.
It was discovered that it is advisable to implement the nozzles, whose coefficient of resistance ranges from 0.5 to 1.1 g/sec*mm2.
In addition, it was determined that degree of dispersion of a liquid jet at the nozzle outlet significantly depends on the liquid pressure at the nozzle inlet, liquid flow rate through the nozzle and surface area of the minimal cross-section of the nozzle. In its turn it was determined that optimal distance between the outlet cross-section of the nozzle and the inlet cross-section of the mixing chamber depends both on the ratio between surface areas of the minimal cross-section of the nozzle and mixing chamber and shape of the dispersed liquid jet behind the nozzle outlet. The jet shape is understood first of all as a degree of atomization of the liquid stream behind the outlet of the nozzle. The most important result of the experiments is that interference of these parameters was uncovered and it became possible to determine more precisely the optimal distance between the outlet cross-section of the nozzle and inlet cross-section of the mixing chamber as well as other optimal dimensions of the liquid-gas ejectors subject to specified operational parameters.
Thus, using the above mentioned formula obtained on the basis of experimental data analysis, it is possible to develop liquid-gas ejectors which have an increased efficiency factor and require minimal energy input for the evacuation of gaseous mediums.